In recent years surgeons have come more and more to the use of surgical staples (sometimes referred to as staple sutures), rather than conventional thread sutures, for the closing of wounds or incisions in the skin of a patient. This is true in part because the use of surgical staples is a far easier procedure. Of even greater importance, however, is the fact that the use of surgical staples is very much faster. Thus, the time required for suturing can be substantially reduced, thereby reducing the length of time the patient must be maintained under anesthesia.
Prior art workers have developed various types of surgical skin staplers. U.S. Pat. No. 3,873,016 teaches a pliers-like surgical stapler exemplary of those wherein the driver engages the forewardmost staple of a row thereof in a magazine and shifts the staple to an anvil and thereafter forms the staple about the anvil. U.S. Pat. Nos. 4,109,844 and 4,178,057 teach surgical stapling instruments of the type provided with an anvil plate having a coextensive, forwardly extending anvil provided with an anvil surface. A row of staples is mounted on the anvil plate and means are provided to constantly urge the row of staples forwardly so that the forwardmost staple of the row is located on the anvil plate. The driver thereafter is used to form the forwardmost staple about the anvil, but no part of the force required of the surgeon is used to shift a staple to the anvil. U.S. Pat. No. 4,411,376 teaches an improved form of anvil plate having forward extensions such that the legs of all of the staples on the anvil plate and anvil are supported except the forwardmost staple in position to be formed and implanted. U.S. Pat. No. 4,485,953 describes a surgical stapling instrument adapted to extract a staple from a separate cartridge thereof and to thereafter form and implant the staple in the skin of the patient.
The above description of surgical skin stapler types is representative only, and is not intended to be exhaustive. Most surgical skin staplers, however, are characterized by similar anvil-driver assemblies in that, during the forming and implanting operation, the anvil is located directly above the wound or incision. The anvil is characterized by a flat anvil surface located substantially parallel to the skin surface of the patient. The anvil surface supports the crown portion of the staple to be formed and implanted.
The typical driver of prior art anvil and driver assemblies has an inverted U-shaped notch formed therein. The U-shaped notch defines parallel bending surfaces adapted to bend the staple legs about the anvil and at the same time implant the staple legs in the skin of a patient. The upper end of the driver notch provides a transverse surface substantially perpendicular to the parallel bending surfaces and extending therebetween. This transverse surface comprises a staple crown-contacting surface which engages the staple crown at the bottom of the driver stroke. The space between the edges of the anvil and the parallel bending surfaces of the driver are such as to tightly accommodate the staple legs. This is true so that the sharpest possible bend is achieved at the juncture between the staple legs and the crown.
The above described interaction between the anvil and the driver has certain drawbacks. For example, the bends produced during the forming procedure at the junctures of the staple legs and the crown are severe and constitute substantially a coining operation. In addition, when the driver returns to its retracted position, the surgical staple has a tendency to be dragged with it. Furthermore, there sometimes is difficulty in slipping the anvil out from under the fully formed and implanted staple. A strong return spring must be used to return the driver to its normal retracted position, since at the completion of the forming and implanting step the staple legs are wedged between the parallel bending surfaces of the driver and the edges of the anvil. Finally, due to natural elastic springback of the wire from which the surgical staple is made, the staple legs tend to separate slightly after release from the driver and anvil so that an absolutely perfectly formed staple is difficult to achieve.
At the present time, the majority of surgical staples are made from metallic wire. Not all surgical staples are made of metallic wire, however. For example, some surgical staples are made of materials which will dissolve in the body environment over a period of time. The present invention will be described in terms of the use of metallic wire staples, but it is to be understood that the invention is applicable to the use of surgical staples made of any appropriate, resilient, permanently deformable material.
The present invention is based upon the discovery that if the anvil surface of the anvil and the staple crown contacting surface of the driver are so configured as to impart a slight concave bow to the crown portion of the staple during the forming and implanting procedure, and if the bow is of such size as to be within the elastic limit of the material from which the staple is made so that the staple crown is not plastically deformed, the junctures of the legs and crown can be slightly overbent so that when the staple crown is released by the driver, it can return to its rectilinear configuration and perfect square bends can be achieved at the junctures of the legs and the crown, producing consistently perfectly formed and implanted staples. In other words, the natural springback of the material from which the staple is made tends to bring the staple into perfect configuration, rather than to spread the staple legs away from a perfect configuration. Additional benefits are also derived from the present invention. For example, greater tolerance can be permitted between the parallel bending surfaces of the driver and the adjacent edges of the anvil. The staple does not have a tendency to be dragged with the driver as the driver is shifted to its normal retracted position and the anvil is more easily slipped from beneath the crown after forming and implanting. Less force is required to form the staple since more generous bends are formed at the juncture of the legs and the staple crown. Since the staple is not wedged between the parallel bending surfaces of the driver and the adjacent edges of the anvil, a return spring having a lesser force can be used to return the driver to its normal retracted position. The teachings of the present invention can be applied to any of the above described types of surgical stapling instruments.
It is known to provide non-surgical staple with a crown portion having a permanent concave bow therein. This is taught, for example, in U.S. Pat. No. 2,351,608. This permanent concave crown bow is provided so that when the staple is driven into a relatively hard workpiece such as wood by a hammer, the hammer blows are applied to the staple at two points substantially in line with the axes of the staple legs. This minimizes bending of the staple legs during the driving operation. The concave shape of the staple crown is permanent and bears no relationship to a forming operation.
U.S. Pat. No. 2,687,061 teaches the use of staples having permanent concave crown portions in a substantially conventional desk-top stapler. The concave crown portion of the staples cooperates with the staple pusher in the magazine in such a way as to reduce the likelihood of staples jamming in the magazine. Again, the concave crown of this reference has nothing to do with staple forming.